U.S. patent number 5,653,552 [Application Number 08/331,211] was granted by the patent office on 1997-08-05 for process for heating an asphalt surface.
This patent grant is currently assigned to McLean Ventures Corporation. Invention is credited to Mostafa Joharifard, Patrick C. Wiley.
United States Patent |
5,653,552 |
Wiley , et al. |
August 5, 1997 |
Process for heating an asphalt surface
Abstract
A process for continuously heating an asphalt surface is
described. The process comprises moving a heater over the asphalt
surface in successive forward and backward directions. The forward
stroke of the heater is effected over a second distance and the
backward stroke of the heater is effected over a first distance.
The ratio of the second distance to the first distance is in the
range of from about 0.10 to about 0.90. Preferably, the heater
comprises at least two independent heaters arranged in series.
Inventors: |
Wiley; Patrick C. (Vancouver,
CA), Joharifard; Mostafa (West Vancouver,
CA) |
Assignee: |
McLean Ventures Corporation
(Vancouver, CA)
|
Family
ID: |
4152046 |
Appl.
No.: |
08/331,211 |
Filed: |
October 28, 1994 |
Foreign Application Priority Data
|
|
|
|
|
Oct 29, 1993 [CA] |
|
|
2102090 |
|
Current U.S.
Class: |
404/77;
404/95 |
Current CPC
Class: |
E01C
23/065 (20130101); E01C 23/14 (20130101) |
Current International
Class: |
E01C
23/14 (20060101); E01C 23/00 (20060101); E01C
23/06 (20060101); E01C 023/14 () |
Field of
Search: |
;404/75,77,79,80,90,91,92,95 ;126/271.1,271.2A |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Lisehora; James A.
Attorney, Agent or Firm: Darby & Darby
Claims
What is claimed is:
1. A process for continuously heating an asphalt surface comprising
the steps of:
(i) providing asphalt surface heating means on said asphalt
surface, the heating means comprising at least two independent
heaters arranged in series;
(ii) translating said heating means a first distance along said
asphalt surface;
(iii) reversing the direction of and translating said heating means
a second distance along said asphalt surface in a direction
substantially opposite to that in Step (ii);
(iv) reversing the direction of and translating said heating means
said first distance along said asphalt surface in a direction
substantially the same as that in Step (ii); and
(v) repeating Steps (iii) and (iv) in a cyclic manner to provide a
heated asphalt surface;
wherein the ratio of the second distance to the first distance is
in the range of from about 0.10 to about 0.90.
2. The process defined in claim 1, wherein the asphalt surface is
heated to a temperature less than about 200.degree. C.
3. The process defined in claim 2, wherein at least one of said
heaters is an infrared heater.
4. The process defined in claim 2, wherein the ratio of the second
distance to the first distance is in the range of from about 0.30
to about 0.90.
5. The process defined in claim 4, wherein each of said independent
heaters is operated at a different temperature.
6. The process defined in claim 5, wherein operation of each of
said independent heaters at a different temperature creates a
temperature gradient as said heating means is translated along the
asphalt surface.
7. The process defined in claim 6, wherein the temperature gradient
is a decrease in operation temperature of each of said independent
heaters.
8. The process defined in claim 7, wherein each of said independent
heaters is operated at a greater temperature in Step (iv) than in
Step (iii).
9. The process defined in claim 4, wherein each of said independent
heaters is connected to provide uniform translation thereof along
the asphalt surface.
10. The process defined in claim 2, further comprising the step of
dispensing an aggregate on said asphalt surface prior to Step
(ii).
11. The process defined in claim 10, wherein the aggregate is
dispensed in the form of a windrow.
12. The process defined in claim 11, wherein Step (ii) further
comprises mixing the aggregate while it is on the asphalt
surface.
13. The process defined in claim 11, wherein Step (ii) further
comprises shifting the aggregate on the asphalt surface to effect
mixing thereof.
14. The process defined in claim 1, wherein the asphalt surface is
heated to a temperature in the range of from about 100.degree. C.
to about 190.degree. C.
15. The process defined in claim 1, wherein the asphalt surface is
heated to a temperature in the range of from about 130.degree. C.
to about 190.degree. C.
16. The process defined in claim 1, wherein at least one of said
heaters is a radiant heater.
17. The process defined in claim 16, wherein the ratio of the
second distance to the first distance is in the range of from about
0.50 to about 0.90.
18. The process defined in claim 17, wherein said heating means
comprises three independent heaters.
19. The process defined in claim 1, wherein at least one of said
heaters is a hot air heater.
20. The process defined in claim 1, further comprising the steps
of:
(vi) rapturing the heated asphalt surface to a depth of at least
about 1.5 inches to provide a ruptured upper surface and an
unruptured surface therebelow;
(vii) mixing the ruptured upper surface while it is on the
unruptured surface to produce a ruptured upper surface which is
substantially free of moisture; and
(viii) pressing the heated, ruptured upper surface to provide a
recycled asphalt surface.
21. The process defined in claim 1, further comprising the steps
of:
(vi) rupturing the heated asphalt surface to a desired depth, the
ruptured surface overlying a remaining unruptured portion of the
asphalt surface;
(vii) mixing at least some of the ruptured surface on the
unruptured portion asphalt surface; and
(viii) pressing the ruptured surface to form a recycled asphalt
surface.
22. A process for continuously heating an asphalt surface
comprising the steps of:
(i) providing asphalt surface heating means comprising a leading
heater and a trailing heater arranged in series on said asphalt
surface;
(ii) translating said heating means a first distance along said
asphalt surface;
(iii) reversing the direction of and translating said heating means
a second distance along said asphalt surface in a direction
substantially opposite to that in Step (ii);
(iv) reversing the direction of and translating said heating means
said first distance along said asphalt surface in a direction
substantially the same as that in Step (ii); and
(v) repeating Steps (iii) and (iv) in a cyclic manner to provide a
heated asphalt surface;
wherein the ratio of the second distance to the first distance is
in the range of from about 0.10 to about 0.90.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for continuously heating
an asphalt surface.
2. Description of the Prior Art
As used throughout this specification, the term "asphalt" is meant
to encompass macadam and tarmac. As is known in the art, asphalt
paved road surfaces typically comprise a mixture of asphalt cement
(typically a black, sticky, petrochemical binder) and an aggregate
comprising appropriately sized stones, gravel and/or sand. The
asphalt concrete mixture is usually laid, compressed and smoothed
to provide an asphalt paved road surface.
Over time, an asphalt paved road surface can deteriorate as a
result of a number of factors. For example, seasonal temperature
fluctuations can cause the road surface to become brittle and/or
cracked. Erosion or compaction of the road bed beneath the road
surface may also result in cracking. Moreover, certain of the
chemical constituents incorporated in fresh asphalt are gradually
lost over time or their properties changed with time, further
contributing to brittleness and/or cracking of the road surface.
Where concentrated cracking occurs, pieces of pavement may become
dislodged. This dislodgement can create traffic hazards, and
accelerates the deterioration of adjacent pavement and highway
substructure. Even if cracking and the loss of pavement pieces do
not occur, the passage of traffic can polish the upper highway
surface, and such a surface can be slippery and dangerous. In
addition, traffic-caused wear can groove, trough, rut and crack a
highway surface. Under wet highway conditions, water can collect in
these imperfections and set up dangerous vehicle hydro-planing
phenomena. Collected water also contributes to the further
deterioration of the pavement.
Prior to about the 1970's, available methods for repairing old
asphalt-paved road surfaces included: spot treatments such as
patching or sealing, paving with new materials over top of the
original surface, and removal of some of the original surface and
replacement with new materials. Each of these methods has inherent
drawbacks and limitations.
Since about the early 1970's, with increasing raw material, oil and
energy costs, there has been a growing interest in trying to
recycle the original asphalt. The world's highways have come to be
recognized as a very significant renewable resource.
Early recycling techniques involved removing some of the original
surface and transporting it to a centralized, stationary recycling
plant where it would be mixed with new asphalt and/or rejuvenating
chemicals. The rejuvenated paving material would then be trucked
back to the work site and laid. These techniques had obvious
limitations in terms of delay, transportation costs and the
like.
Subsequently, technology was developed to recycle the old asphalt
at the worksite in the field. Some such processes involved heating
and are frequently referred to as "hot-in-place recycling"
(hereinafter referred to as HIPR).
This technology comprises many known processes and machines in the
prior art for recycling asphalt paved surfaces where the asphalt
has broken down. Generally, these processes and machines operate on
the premise of (i) heating the paved surface (typically by using
large banks of heaters) to facilitate softening or plasticization
of an exposed layer of the asphalt; (ii) mechanically breaking up
(typically using devices such as rotating, toothed grinders; screw
auger/mills; and rake-like scarifiers) the heated surface; (iii)
applying fresh asphalt or asphalt rejuvenant to the heated, broken
asphalt; (iv) distributing the mixture from (iii) over the road
surface; and (v) compacting or pressing the distributed mixture to
provide a recycled asphalt paved surface. In some cases, the
heated, broken material can be removed altogether from the road
surface, treated off the road surface and then returned to the
surface and pressed into finished position. Much of the prior art
relates to variations of some kind on this premise.
Over time, HIPR has had to address certain problems, some of which
still exist today. For example, asphalt concrete (especially the
asphalt cement within it) is susceptible to damage from heat. Thus,
the road surface has to be heated to the point where it was
sufficiently softened for practical rupturing, but not to the point
of harming it. Furthermore, it was recognized that asphalt concrete
is increasingly hard to heat as the depth of the layer being heated
increases. Another problem results from excess and/or smoking of
the asphalt surface which can lead to a negative impact on the
environment. Many patents have attempted to address these
problems.
U.S. Pat. No. 3,361,042 (Cutler), the contents of which are
incorporated herein by reference, discloses a process for road
surfacing. The process comprises the steps of: heating the road
surface in a non-oxidizing environment; scarifying the heated
surface deeply; piling the scarified material in windrows; heating
the piled windrows in a non-oxidizing atmosphere; initially
planing, levelling and kneading the heated mixture; adding minor
amounts of conventional tack coat; finally planing, levelling and
kneading the mixture; tamping and screeding the mixture; and
compacting the mixture. The steps of initial and final planing,
levelling and kneading of the mixture may be repeated during or
omitted from the process.
U.S. Pat. No. 3,970,404 (Benedetti), the contents of which are
incorporated herein by reference, discloses a method of
reconstructing asphalt pavement. Generally, the method comprises
heating the asphalt surface in successive stages during timed
intervals. This gradual heating apparently permits the heat to
penetrate the asphalt more deeply with minimal or no overheating
thereof. The heated asphalt is then scarified to a depth not
greater than that to which it has been heated. The scarified
asphalt is then worked to provide a recycled asphalt surface. This
method is somewhat inefficient since scarifying is effected only
when the heat has penetrated the asphalt surface to a desired
depth. As is well known in the art, in certain instances, the depth
of heat penetration is directly related to the square root of the
time provided for heat penetration, i.e. -- 25 seconds may be
required for the heat to penetrate to a depth of 5 millimeters
while 49 seconds may be required for the heat to penetrate to a
depth of 7 millimeters. Thus, increasing the time allowance for
desired heat penetration results in a decrease in overall process
efficiency.
U.S. Pat. No. 3,843,274 (Gutman et al. ), the contents of which are
incorporated herein by reference, discloses an asphalt reclaimer.
Generally, the reclaimer is adapted to carry out the following
steps: heating the asphalt surface, cutting the heated surface,
conveying the cut surface away from the road to a pugmill,
pulverizing the cut surface in the pugmill, redistributing the
pulverized asphalt back onto the road surface and levelling the
redistributed asphalt to provide a recycled asphalt surface.
U.S. Pat. No. 3,989,401 (Moench), the contents of which are
incorporated herein by reference, discloses an apparatus for
renewing or reconditioning asphaltic pavement surfaces. Generally,
the apparatus comprises a hood and burner assembly which heats a
surface over which it is moved, a scarifying assembly that scrapes,
breaks up and distributes the heated surface material and a
levelling assembly that levels the scarified surface and material.
This reference does not disclose or suggest processing of the
scarified material to rejuvenate it in place.
U.S. Pat. No. 4,011,023 (Cutler), the contents of which are
incorporated herein by reference, discloses a machine for recycling
macadam highway pavement. The subject machine is intended to be
used on a pavement surface which has been previously scarified or
dislodged. This loose material is removed from the road surface,
thereafter heated, mixed with fresh asphalt and spread on the
original roadbed site. Heating is conducted off the road surface in
a special chamber using a complicated multi-directional conveyor
system. This machine is cumbersome and deficient since it requires
complicated and expensive conveyors to remove the surface to be
recycled from the road, to heat the removed material and reapply it
thereafter.
U.S. Pat. No. 4,124,325 (Cutler), the contents of which are
incorporated herein by reference, discloses a method and apparatus
for recycling asphalt concrete roadways. Essentially, the process
comprises heating the pavement surface with propane fired emitters;
scarifying the heated surface to penetrate and excavate the entire
surface to a depth of approximately 3/4 inch; applying asphalt over
the heated, scarified surface; mixing the excavated material;
commingling the excavated material with additional hot mix in a
pugmill rotor; and levelling the mix from the pugmill rotor on the
roadway to provide a recycled asphalt surface.
U.S. Pat. Nos. 4,129,398 and 4,335,975 (both to Schoelkopf), the
contents of each of which are incorporated herein by reference,
disclose a method and apparatus for plastifying and tearing up of
damaged road surfaces and covers. The method comprises plastifying
(heating) and breaking up the road surface with first and second
separate and distinct devices. The second device also serves the
purpose of distributing, rearranging and profiling the broken-up
material on the road surface in the absence of fresh asphalt being
applied to the road surface. Thereafter, a third separate and
distinct device is used to apply fresh asphalt or other bituminous
material onto the broken-up, distributed, rearranged and profiled
top surface of the road.
U.S. Pat. No. 4,226,552 (Moench), the contents of which are
incorporated herein by reference, discloses an asphaltic pavement
treatment apparatus and method. Generally, the method comprises
heating and scarifying the asphalt surface to form a loose
aggregate-asphaltic mixture on the ground surface. This mixture is
then removed from the ground surface, heated, thoroughly mixed with
a conditioner for the asphalt and reapplied to the ground surface
as a mat. This method is inefficient since each treatment is
carried out by an independently operable, portable apparatus and
since the asphaltic must be removed from the road surface for
reconditioning.
U.S. Pat. No. 4,534,674 (Cutler), the contents of which are
incorporated herein by reference, discloses a dual lift repaving
machine. The machine includes, in series: a preliminary heater; a
preliminary scarifier; a main heater; a main scarifier; a sprayer
for spraying liquid asphalt cutback onto the heated, scarified road
surface; a first macadam dispensing device to dispense hot mix onto
the sprayed, heated, scarified road surface; a first mixer for
commingling the hot mix and the sprayed, heated, scarified road
surface; a first screed to level and partly compact the material to
form the first lift; a second macadam dispensing device to dispense
additional hot mix onto the road surface; a second mixer for mixing
the hot mix in situ; and a second screed to level and compact the
new hot mix to provide a second road lift. The necessity of
providing two lifts renders this machine complicated to use and
relatively expensive to acquire.
U.S. Pat. No. 4,545,700 (Yates), the contents of which are
incorporated herein by reference, discloses a process for recycling
asphalt pavement. Essentially, the process purports to overcome the
difficulties associated with inefficient heat penetration into the
asphalt surface by providing steps of serially heating and milling
multiple layers of the asphalt surface until the desired depth of
asphalt has been removed and then, optionally, mixing the heated
asphalt with additives. Typically, each heating/milling step
results in removal of a strip which is at least 1/4 inch deep. This
process requires the use of many heaters and millers which are
complicated and expensive machines.
U.S. Pat. No. 4,711,600 (Yates), the contents of which are
incorporated herein by reference, discloses a heating device for
use with asphalt pavement resurfacing equipment. The only example
of resurfacing equipment disclosed is an apparatus in which layers
of the road surface are successively heated, milled and removed
from the road surface, via conveyors, for mixing with fresh asphalt
or asphalt rejuvenant, and subsequent reapplication to the road
surface. The use of a plurality of conveyors can be problematic
since it adds excessive cost and complexity to the task at
hand.
U.S. Pat. No. 4,784,518 (Cutler), the contents of which are
incorporated herein by reference, discloses a double-stage repaving
method and apparatus. The subject method includes a first stage
comprising the steps of: heating an upper layer of an asphalt
surface; scarifying the heated upper layer; adding recycling agent
to the upper layer and thoroughly mixing and screeding the mixture
to form recycled material; and adding fresh asphalt to the recycled
material and milling the combination to form a mixed material
thereby leaving exposed a lower layer of asphalt material. The
second stage in the method comprises: conveying the mixed material
from the first stage away to a paving station at the end of the
process; subjecting the exposed lower layer of asphalt material to
the same heating, scarifying, treatment and working steps to which
the upper layer was subject; and laying the mixed material down on
the exposed road surface (i.e. upper and lower asphalt layers
removed) to provide a recycled road surface. This method is
deficient as it requires the use of two relatively expensive and
complicated conveyors.
U.S. Pat. No. 4,793,730 (Butch), the contents of which are
incorporated herein by reference, discloses a method and apparatus
for asphalt surface renewal. Generally, the method comprises the
steps of: steam heating the asphalt surface; breaking the heated
surface to a depth of about two inches and thoroughly mixing in
situ lower material in the asphalt with the broken material;
further steam heating the material to fuse the heated mixture into
a homogeneous surface; screeding the homogeneous surface; and
compacting the screed surface. The method and apparatus purportedly
can be used to resurface asphaltic paving surfaces without
requiring the addition of new materials or rejuvenants.
U.S. Pat. No. 4,929,120 (Wiley et al.), the contents of which are
incorporated herein by reference, discloses a two-stage process for
rejuvenating asphalt-paved road surfaces. In the first stage of the
process, the entire width of the original asphalt surface is heated
to a depth of about 1 inch and a temperature of about 200.degree.
C. The heated upper surface is then removed completely from the
road surface (using scarifying, windrowing and conveying
techniques) to expose a lower asphalt surface corresponding to the
entire width of the original asphalt surface. In the second stage
of the process, the lower asphalt surface is heated to a depth of
about 1 inch and a temperature of about 200.degree. C. The heated
lower surface is then ruptured (e.g. scarified) and either left in
place or completely removed from the road surface. If the ruptured
lower surface is left in place, asphalt from the upper layer and,
optionally, fresh asphalt (or asphalt rejuvenant) is applied
thereover. Alternatively, if the ruptured lower surface is
completely removed it may be commingled with asphalt from the upper
layer and, optionally, fresh asphalt (or asphalt rejuvenant), and
thereafter returned to the road surface. Finally, pressure is
applied to force the upper/lower layer mixture against the road
surface to provide a smooth, recycled surface. This process is
somewhat deficient since it requires removal of at least the upper
portion of the asphalt surface necessitating the use of relatively
expensive and complicated equipment.
U.S. Pat. No. 4,850,740 (Wiley), the contents of which are
incorporated herein by reference, discloses a method and apparatus
for preparing asphaltic pavement for repaving. This patent
purportedly provides an improvement over U.S. Pat. No. 4,929,120 by
eliminating the need to remove the upper layer of heated, scarified
asphalt completely away from the road surface prior to treatment of
the lower layer of asphalt. Essentially, the improvement relates to
heating, scarifying and windrowing the asphalt surface in a manner
to provide a central strip comprising windrowed material from outer
strips of the asphalt surface piled onto an untreated (i.e. not
scarified/removed) central strip of the asphalt surface. The
central strip is then ground to mix the centrally windrowed
material with the previously unground central strip of the asphalt
surface. This mix is then spread over the entire asphalt surface
and pressed into place. This process is somewhat deficient since it
requires two separate and distinct grinding steps.
As is apparent from the foregoing, many efforts have been made in
the prior art to deal with the inherent difficulty of adequately
and uniformly heating an asphalt surface in an efficient manner
while minimizing or eliminating burning and smoking of the asphalt
surface. To the Applicant's knowledge, much of this effort has
involved utilizing relatively complicated means to distribute heat
through the asphalt surface after rupturing thereof. This has
involved treating the ruptured surface on or off the asphalt
surface, and thereafter reapplying and pressing the ruptured
surface to create a recycled asphalt surface. For example, it is
believed that most of the prior art techniques require further
heating of the ruptured asphalt surface to facilitate heat
distribution therethrough. Such complicated processing means are
typically cumbersome and large yet are necessary due to the
inability to preheat the unruptured asphalt surface adequately
without overheating thereof. Further, the need for complicated
processing means increases the capitol cost associated with the
process and dictates the need for highly skilled operators.
It would be desirable to have a process of heating an asphalt
surface in a manner which facilitated subsequent recycling thereof.
Ideally, such an asphalt surface heating process could be conducted
utilizing conventional asphalt heaters and coupled with a
relatively simple recycling system to provide a recycled asphalt
surface. Preferably, the process would be capable of heating the
unruptured asphalt surface to a sufficient extent such that the
requirement further heating after rupturing could be obviated or
mitigated. This would result in the ability to reduce the amount of
equipment necessary to effect recycling of the asphalt surface and
thereby reduce the capital cost associated with the overall
recycling process.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a novel process
for heating an asphalt surface.
It is another object of the present invention to provide a process
for heating an asphalt surface which obviates or mitigates at least
one of the foregoing disadvantages of the prior art.
The present inventors have discovered that it is possible to
achieve relatively uniform and efficient heating of an asphalt
surface to a desired depth if preheating of the asphalt surface is
accomplished in a particular manner. Generally, it has been
discovered that vastly improved preheating of the asphalt surface,
with minimal or no overheating thereof, can be achieved by
reciprocating the motion of heating. More specifically, by
cyclically translating the heating means over the asphalt surface a
first distance and thereafter backtracking the heating means a
second distance which is less than the first distance, the asphalt
surface may be heated uniformly to a desired depth in an efficient
manner. By preheating the asphalt surface in this manner, it has
been further discovered that heating can be accomplished
efficiently, relatively uniformly and to a desired depth while
obviating or mitigating damage to the asphalt surface associated
with overheating thereof. Further, the present process can be used
while minimizing or eliminating burning and/or smoking of the
asphalt surface.
Accordingly, in one of its aspects, the present invention provides
a process for continuously heating an asphalt surface comprising
the steps of:
(i) providing asphalt surface heating means on the asphalt
surface;
(ii) translating the heating means a first distance along the
asphalt surface;
(iii) reversing the direction of and translating the heating means
a second distance along the asphalt surface in a direction
substantially opposite to that in Step (ii);
(iv) reversing the direction of and translating the heating means a
first distance along the asphalt surface in a direction
substantially the same as that in step (ii); and
(v) repeating Steps (iii) and (iv) in a cyclic manner to provide a
heated asphalt surface;
wherein the ratio of the second distance to the first distance is
in the range of from about 0.10 to about 0.90.
In another of its aspects, the present invention provides a process
for continuously heating an asphalt surface comprising the steps
of:
(i) providing asphalt surface heating means comprising a leading
heater and a trailing heater arranged in series on the asphalt
surface;
(ii) translating the heating means a first distance along the
asphalt surface;
(iii) reversing the direction of and translating the heating means
a second distance along the asphalt surface in a direction
substantially opposite to that in Step (ii);
(iv) reversing the direction of and translating the heating means a
first distance along the asphalt surface in a direction
substantially the same as that in Step (ii); and
(v) repeating Steps (iii) and (iv) in a cyclic manner to provided a
heated asphalt surface;
wherein the ratio of the second distance to the first distance is
in the range of from about 0.10 to about 0.90.
Preferably, in this embodiment of the invention, the heating means
further comprises at least one intermediate heater between the
leading heater and the trailing heater.
In a preferred aspect of the invention, the process further
comprises the steps of:
(vi) rupturing the heated asphalt surface to a depth of at least
about 1.5 inches to provide a ruptured upper surface and an
unruptured surface therebelow;
(vii) mixing the ruptured upper surface while it is on the
unruptured surface to produce a ruptured upper surface which is
substantially free of moisture; and
(viii) pressing the heated, ruptured upper surface to provide a
recycled asphalt surface.
In yet a further preferred aspect of the present invention, the
process further comprises the steps of:
(vi) rupturing the heated asphalt surface to a desired depth, the
ruptured surface overlying a remaining unruptured portion of the
asphalt surface;
(vii) mixing at least some of the ruptured surface on the
unruptured portion asphalt surface; and
(viii) pressing the ruptured surface to form a recycled asphalt
surface.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the present invention will be described with
reference to the accompanying drawings, in which:
FIG. 1 is a graphic illustration of the temperature/time
relationship for a conventional asphalt heating process and the
present process;
FIG. 2 is a graphic illustration of the temperature/time
relationship for an asphalt surface at various depths utilizing the
present process;
FIG. 3 (comprising FIGS. 3A and 3B) is an illustration of a remixer
capable of being used in conjunction with the present process;
and
FIG. 4 (comprising FIGS. 4A and 4B) is an illustration of the
embodiment of the invention where an aggregate is heated with the
asphalt surface.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
One of the advantages accruing from the present process is the
ability to use conventional asphalt surface heaters to effect, in
some cases, all of the heating necessary for recycling prior to
rupture of the asphalt surface. Thus, the choice of asphalt surface
heating means is not particularly restricted and use may be made of
radiant heaters (e.g. infrared heaters), hot air heaters,
convection heaters, microwave heaters, direct flame heaters and the
like. Generally, the heater is an independent, self-propelled
vehicle which comprises a series of rows of elongate heaters
extending transversely across the asphalt surface. The preferred
heating means for use in the present process is a series of propane
or diesel fired infrared heaters. Such heaters are well known in
the art.
Generally, it is preferred that the vehicular heating means used in
the present process may be readily switched from forward to reverse
operation, and vice versa. The manner by which this is accomplished
is not particularly restricted and is within the purview of those
of skill in the art.
The asphalt surface heating means is: moved forward a first
distance; reversed; and thereafter moved backward in an opposite
direction a second distance. The ratio of the second distance to
the first distance is in the range of from about 0.10 to about
0.90. Thus, when the ratio is 0.90, for every 10 units of distance
the asphalt surface heating means is moved forward, it is moved
backwards 9 units of distance. Similarly, when the ratio is 0.10,
for every 10 units of distance the asphalt surface heating means is
moved forward, it is moved backwards 1 unit of distance.
Preferably, the ratio of the second distance to the first distance
is in the range of about 0.30 to about 0.90, more preferably in the
range of from about 0.50 to about 0.90.
It is well known in the art that overheating of the asphalt surface
must be avoided since this can result in ignition of and/or damage
to the asphalt surface. Specifically, it is well known in the art
that an asphalt mixture to a temperature above about 160.degree. C.
can result in damage to the asphalt cement. It is also well known
in the art that the surface of asphalt pavement in need of recycle
may heated to a temperature approaching the flashpoint of the
asphalt since, typically, the surface oil has been worn off, washed
away or severly oxidized. Typically, the flash point of an asphalt
surface is at a temperature exceeding about 210.degree. C. Using
the process of the present invention, it is possible to heat an
unruptured asphalt surface to a temperature close to but not
exceeding the flash point of the asphalt surface. Moreover, it is
possible to maintain the unruptured asphalt surface at
substantially this temperature. Thus, it is particularly preferred
in the present process that the asphalt surface is heated to a
temperature less than about 200.degree. C., more preferably a
temperature in the range of from about 100.degree. C. to about
190.degree. C., most preferably in the range of from about
130.degree. C. to about 190.degree. C.
The ability to achieve such uniform and steady-state heating of the
asphalt surface is illustrated in FIG. 1. Specifically, curve A is
a representative temperature/time relationship associated with
passing an infrared heater over an asphalt surface in the
conventional manner (i.e. moving the heater in a single direction
at a substantially constant speed). As is apparent, the temperature
of the asphalt surface peaks between 2 and 3 minutes after
initiating of heating to a temperature above the flashpoint of the
asphalt surface. In comparison, curve B is representative of the
temperature/time relationship obtained using the process of the
present process (i.e. reciprocating movement of the heater in an
unbalance manner). As illustrated, the temperature of the asphalt
surface is increased to but does not exceed 200.degree. C., i.e.
below the flashpoint of the asphalt surface.
This point is further illustrated with reference to FIG. 2 which
provides individual temperature/time relationship curves for the
asphalt surface at the following depths: 0 cm, 1 cm, 2 cm, 3 cm, 4
cm and 5 cm. As can be seen, the temperature varies from
200.degree. C. at 0 cm (on the asphalt surface itself) to
80.degree. C. 5 centimeters (approximately 2 inches) below the
surface. The average temperature of the 5 centimeter layer is
approximately 120.degree. C. This time/temperature profile is
highly advantageous and simplifies recycling of the asphalt
surface.
A particularly preferred embodiment of the present invention is the
use of an asphalt surface heating means comprising at least two
independent heaters. Ideally, the heaters are arranged in series,
with a leading heater and a trailing heater. More preferably, at
least one intermediate heater is disposed between the leading
heater and the trailing heater. When two or more independent
heaters are used, it is preferred that the above-described uneven
reciprocating translation thereof is conducted in a uniform
manner.
When two or more independent heaters are used in the present
process, it is preferred that they be connected to each other to
facilitate uniform translation of all of the heaters.
It is further preferred that, when two or more independent heaters
are used, each heater be operated at a different temperature.
Further, it is preferred that operation of the independent heaters
at a different temperature creates a temperature gradient (i.e. of
the heat output by the heaters) as the heating means in its
entirety is translated along the asphalt surface. More preferably,
the temperature gradient is a decrease in operation temperature of
from leading heater to the trailing heater. A particularly
advantageous manner of utilizing the temperature gradient
associated with this embodiment of the invention is, for each
independent heater, to vary the temperature depending on whether
the heater is being translated in Step (iii) (i.e. relatively
backward stroke) or Step (iv) (i.e. relatively forward stroke).
Specifically, for each independent heater, it is most preferred, to
have greater heater operational temperature in relatively forward
stroke than the heater operational temperature in the relatively
backward stroke while maintain the overall preferred temperature
gradient between individual heaters.
One of the key advantages of the present process is that it may
comprise the entire heating requirement in the overall asphalt
surface recycling process. Thus, while it is contemplated that the
present process may be used in conjunction with many of the prior
art processes described above, it may also be utilized with a
greatly simplified remixer which is devoid of heaters. This is
believed to be a significant advance in the art.
While the choice of remixer is not particularly restricted, a
preferred remixer is depicted in FIG. 3. In FIG. 3, the remixer is
shown in a top schematic view in FIG. 3A and side elevation in FIG.
3B. Thus, a remixer is illustrated generally at 10. The leading
portion of remixer 10 comprises a dump truck 20 connected to a
hopper 30 which is attached to a grinder/mixer shown generally at
40. Grinder/mixer 40 comprises a pair of leading grinders 50 and a
trailing grinder 60 such that the overall effect of grinders 50 and
60 is to traverse the asphalt surface to be recycled. Trailing
grinder 60 is connected to a pugmill 70 which, in turn, is
connected to a conveyor 80. Below conveyer 80, there is disposed a
repave screed 90. The trailing portion of grinder/mixer 40 is
connected to a paver 100. Paver 100 serves to propel itself and
grinder/mixer 40 in unison with dump truck 20. The trailing portion
of paver 100 comprises a screed 110.
In use, dump truck 20 would be loaded with fresh asphalt and/or
asphalt rejuvenant and, in unison with grinder/mixer 40 and paver
100, would be propelled behind the heater or heaters used in the
present process. The fresh asphalt/asphalt rejuvenant is dispensed
from dump truck 20 via hopper to the heated asphalt surface. It
will be appreciated that the fresh asphalt/asphalt rejuvenant may
be optionally preheated prior to application to the heated asphalt
surface. The heated asphalt surface, with the fresh asphalt/asphalt
rejuvenant lying thereon, is then ground in place by grinders 50
and 60, and thereafter is thoroughly mixed in pugmill 70.
Thereafter, the thoroughly mixed product exiting pugmill 70 is
lifted off the unruptured surface via conveyor 80 while repave
screed 90 serves to level the unruptured surface. The mixed product
is reapplied to the unruptured asphalt surface and pressed into
place by screed 110 on the trailing portion of paver 100.
It will be apparent to those of skill in the art that many
variations may be made to this embodiment of the invention while
maintaining the advantages associated therewith. For example, it
may be possible to added the fresh asphalt at a more downstream
point rather than prior to operation of grinder/mixer 40. Further,
in certain applications, it may be possible to omit dump truck 20
and its contents in favour of a 100% recycle process.
Alternatively, in other applications, sufficient recycling may be
obtaining simply by adding oil, optionally preheated, before or
during the operation of grinder/mixer 40.
A particularly preferred application of the present process is that
it may be used in conjunction with a modified form of the process
and apparatus described in published International (PCT) patent
application No. WO 93/17185, the contents of which are incorporated
herein by reference. In this published International patent
application, a process is described which comprises, inter alia,
heating and mixing a ruptured asphalt surface without the need to
remove the ruptured surface or use complicated windrowing
techniques to achieve uniform heating thereof. The present
inventors have now discovered that it is possible to use the
present process with the process described in the published
International patent application. More beneficially, the present
inventors have discovered that the present process may be used with
a more simplified version of the process described in published
International patent application No. WO 93/17185. Specifically, it
is contemplated that the requirement for cyclical heating and
mixing as described in the published International application is
not required due to ability of the present process to heat an
unruptured asphalt surface in an efficient manner to a desired
temperature and depth without overheating thereof. This allows for
modifying the process in the published International patent
application to do without the heaters interposed between the
mixers.
Thus, the present process, in a preferred embodiment, comprises the
further steps of:
(vi) rupturing the heated asphalt surface to a depth of at least
about 1.5 inches to provide a ruptured upper surface and an
unruptured surface therebelow;
(vii) mixing the ruptured upper surface while it is on the
unruptured surface to produce a ruptured upper surface which is
substantially free of moisture; and
(viii) pressing the heated, ruptured upper surface to provide a
recycled asphalt surface.
Further, the present process, in another preferred embodiment,
comprises the further steps of:
(vi) rupturing the heated asphalt surface to a desired depth, the
ruptured surface overlying a remaining unruptured portion of the
asphalt surface;
(vii) mixing at least some of the ruptured surface on the
unruptured portion asphalt surface; and
(viii) pressing the ruptured surface to form a recycled asphalt
surface.
The rupturing, mixing and pressing described in Steps (vi), (vii)
and (viii), respectively, in both of the foregoing embodiments may
be conducted using the techniques and equipment described in
published International patent application No. WO 93/17185, the
contents of which are incorporated herein by reference.
Depending on the nature of the overall recycling process (e.g.
condition of asphalt surface, speed at which the equipment will be
passing over the asphalt surface, the temperature at which the
heaters are operated, the number of heaters, etc.), supplementary
heaters may be used after rupturing in Step (vi) in either of the
foregoing preferred embodiments.
Another preferred aspect of the present process comprises the step
of dispensing an aggregate on the asphalt surface prior to heating
thereof. Preferably, the aggregate is dispensed in the form of a
windrow. The process is then carried out as described above such
that both the asphalt surface and the windrow of aggregate are
heated.
This embodiment of the present process is illustrated in FIG. 4.
FIG. 4 is comprised of FIGS. 4A (a top schematic view) and 4B (a
side view of the process) which are aligned to depict the same
process.
Thus, there is illustrated a dump truck 200 leading a hopper 210.
Trailing hopper 210 is a leading asphalt surface heater 220 which
comprises three banks of infrared heaters 221, 222 and 223.
Trailing asphalt surface heater 220 is an intermediate asphalt
surface heater 230 which similarly comprises three banks of
infrared heaters 231, 232 and 233. After asphalt surface heater 230
is a trailing asphalt surface heater 240 which comprises three
banks of infrared heaters 241, 242 and 243. After asphalt surface
heater 240 there is a grinder/mixer 250 connected to a paver 260.
Grinder/mixer 250 and paver 260 are similar to the grinder/mixer
(40) and paver (100) described hereinabove with reference to FIG.
4.
In use, dump truck 200 would be loaded with a suitably sized
aggregate and propelled, in unison, with hopper 210. As dump truck
200 and hopper 210 are propelled, aggregate is dispensed from dump
truck 200 to hopper 210 and is formed into a windrow 270 on the
(unheated) asphalt surface. Thereafter, leading asphalt surface
heater 220 is passed over the asphalt surface/aggregate windrow in
a reciprocating manner as depicted by arrows 280. Next,
intermediate asphalt surface heater 230 passes over the asphalt
surface/aggregate windrow in a reciprocating manner as illustrated
by arrows 290. Further, as shown, trailing bank of heaters 231,
there is a cylindrical broom 300 which serves to shift the
aggregate windrow sideways by approximately one windrow width.
Preferably, cylindrical broom 300 is lowered when intermediate
asphalt surface heater 230 is moved in a forward direction (i.e.
toward dump truck 200) and raised when it is moved in a rearward
direction (i.e. toward paver 260). Thereafter, trailing asphalt
surface heater 240 passes over the asphalt surface/aggregate
windrow in a reciprocating manner as depicted by arrows 310.
Trailing bank of heaters 242 is a cylindrical broom 320 which
operates similarly to cylindrical broom 300 but serves to shift
aggregate windrow 270 to the opposite side of the asphalt surface.
Finally, the recycling process is completed by grinder/mixer 250
and paver 260 in a manner similar to that described above with
reference to FIG. 4.
As will be appreciated, many variations of the disclosed process
are possible without deviating from the spirit and substance
thereof. Accordingly, while this invention has been described with
reference to illustrative embodiments, this description is not
intended to be construed in a limiting sense. Various modifications
of the illustrative embodiment as well as other embodiments of the
invention will be apparent to persons skilled in the art upon
reference to this disclosure. It is therefor contemplated that the
dependant claims with cover any such modifications or
embodiments.
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